The present invention relates to a positive photosensitive resin composition which can form a pattern of high resolution and high residual film ratio and has high sensitivity.
Polyimide resins excellent in heat resistance, electrical properties, mechanical properties, etc. have heretofore been used in the surface-protecting film or interlayer dielectric of a semiconductor device. In recent years, however, significant improvements in heat cycle resistance, thermal shock resistance, etc. have become necessary for the resins used in the above applications, because semiconductor devices have come to employ a higher integration and a larger size, packages have become thinner and smaller, and the mounting has shifted to surface mounting by solder reflow. Therefore, a resin of higher performance has come to be required.
Meanwhile, a technique of allowing a polyimide resin to have photosensitivity by itself is drawing attention. The polyimide resin allowed to have photosensitivity by such a technique, includes, for example, a photosensitive polymide resin represented by the following formula (12): 
With such a resin, the step of pattern formation can be partly simplified and a shorter step and a higher yield are achieved. However, a solvent such as N-methyl-2-pyrrolidone or the like is required in the step of development, which incurs a problem in safety and handling.
Hence, there have recently been developed positive photosensitive resin compositions which can be subjected to development with an aqueous alkali solution. For example, there is disclosed, in JP-B-1-46862, a positive photosensitive resin composition constituted by a polybenzoxazole precursor, which is a base resin, and a diazoquinone compound, which is a photosensitizer. This resin composition has high heat resistance, excellent electrical properties and fine pattern formability and has a possibility of being used as a resin for wafer coating as well as for interlayer insulation. The development mechanism of this positive photosensitive resin composition is as follows. The diazoquinone compound is insoluble in an aqueous alkali solution when unexposed to a light; when exposed to a light, the diazoquinone compound gives rise to a chemical reaction to become soluble in the aqueous alkali solution; and by utilizing such difference in solubility between when exposed and when unexposed, the exposed portion is dissolved and removed, whereby a film pattern consisting of only the unexposed portion can be formed.
When these photosensitive resin compositions are used practically, particularly important is the sensitivity of each photosensitive resin composition. A low sensitivity requires a long exposure time, resulting in a low throughput. When the base resin is allowed to have a smaller molecular weight as a means for increasing the sensitivity of the photosensitive resin composition, the unexposed portion gives a large film thickness loss during development, which makes it impossible to obtain a required film thickness or incurs the collapse of pattern shape. Therefore, it is highly desired to develop a photosensitive resin composition which satisfies the above-mentioned properties and yet has high sensitivity.
The present invention aims at providing a positive photosensitive resin composition which can form a pattern of high resolution and high residual film ratio and has high sensitivity.
The present invention lies in a positive photosensitive resin composition comprising:
100 parts by weight of (A) a polyamide resin represented by the following general formula (1), and
1 to 50 parts by weight of (B1) a photosensitizer which is a 1,2-naphthoquinone-2-diazide-5-sulfonate or a 1,2-naphthoquinone-2-diazide-4-sulfonate, of a phenol compound having a skeletal structure represented by the following general formula (2): 
wherein X is a tetravalent cyclic compound group; Y is a divalent cyclic compound group; Z is a group represented by 
wherein R1 and R2 are each a divalent organic group, and R3 and R4 are each a monovalent organic group; E is an aliphatic group or a cyclic compound group, each having at least one alkenyl or alkynyl group; a and b each show a molar fraction, a+b=100 mole %, a=60 to 100 mole %, and b=0 to 40 mole %; and n is an average value and a positive number of 2 to 300, and 
wherein R5 is one atom or group selected from hydrogen atom, alkyl groups, alkoxy groups, aryl groups and substituted aryl groups; a plurality of R6""s may be the same or different and are each one atom or group selected from hydrogen atom, hydroxyl group, alkyl groups, alkoxy groups, aryl groups and cycloalkyl groups, and at least one R6 is hydroxyl group; a plurality of R7""s may be the same or different and are each one atom or group selected from hydrogen atom, hydroxyl group, alkyl groups, alkoxy groups, aryl groups and cycloalkyl groups, and at least one R7 is hydroxyl group; l is an integer of 0 to 3; m is an integer of 1 to 3; and n is an integer of 1 to 3.
The polyamide resin of the general formula (1) is obtained by reacting a bis(aminophenol) having an X structure, a silicone diamine having a Z structure which is optionally used, a dicarboxylic acid or its dichloride, having a Y structure, and an acid anhydride which generates an E structure upon reaction with amino group. In order to obtain a higher yield, etc., it is possible to use a dicarboxylic acid derivative of active ester type obtained by reaction of a dicarboxylic acid with 1-hydroxy-1,2,3-benztriazole or the like. The polyamide resin, when heated at about 300 to 400xc2x0 C., gives rise to dehydration and ring closure to become a polybenzoxazole which is a heat-resistant resin.
The X of the polyamide resin of the general formula (1) used in the present invention includes, for example, the followings but is not restricted thereto. 
In the above, A is xe2x80x94CH2xe2x80x94, xe2x80x94C(CH3)2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94NHCOxe2x80x94 or xe2x80x94C(CF3)2xe2x80x94.
Among them, particularly preferred one is selected from the followings. 
The Y of the polyamide resin of the general formula (1) includes, for example, the followings but is not restricted thereto. 
In the above, A is xe2x80x94CH2xe2x80x94, xe2x80x94C(CH3)2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94NHCOxe2x80x94 or xe2x80x94C(CF3)2xe2x80x94.
Among them, particularly preferred one is selected from the followings. 
The E of the polyamide resin of the general formula (1) includes, for example, the followings but is not restricted thereto. 
Among them, particularly preferred one is selected from the followings. 
In the present invention, a dicarboxylic acid or its dichloride, or its derivative having a Y structure is reacted with a bis(aminophenol) having an X structure to synthesize a polyamide resin; thereafter, each of the terminal amino groups of the polyamide resin is capped with an acid anhydride having at least one alkenyl or alkynyl group shown in the E of the general formula (1).
The Z of the polyamide resin of the general formula (1) which is used optionally, includes, for example, the followings but is not restricted thereto. 
The Z of the general formula (1) is used, for example, when very high adhesion to a substrate (e.g. silicon wafer) is required. The proportion b of Z used is at most 40 mole %. A proportion of larger than 40 mole % is not preferred, because the resulting resin has very low solubility and generates scum after development, making pattern formation impossible. Each of the X, Y, E and Z may be used in one kind or admixture of two or more kinds.
The n of the general formula (1) is an average value and a positive number of 2 to 300. An n of larger than 300 is not preferred because scum may appear after development.
The examples of the phenol compound which is a skeleton of the photosensitizer (B1) used in the present invention, include the followings but are not restricted thereto. 
In the phenol compound of the general formula (2) constituting the photosensitizer (B1) used in the present invention, it is preferred that 20 to 80% of the hydroxyl groups is substituted into a 1,2-naphthoquinone-2-diazide-5-sulfonate or a 1,2-naphthoquinone-2-diazide-4-sulfonate. When the proportion of substitution of the hydroxyl groups is less than 20%, it is impossible to sufficiently inhibit the dissolution of the polyamide resin represented by the general formula (1) and it is impossible to obtain a desired film thickness after development. When the proportion is more than 80%, scum may generate after development at the bottom of the pattern formed. Therefore, such proportions are not preferred. Incidentally, the proportion of substitution is a proportion of substituted hydroxyl groups to the total amount of the hydroxyl groups possessed by the phenol compound represented by the general formula (2). In the present invention, the amount of the photosensitizer (B1) added to the polyamide resin (A) represented by the general formula (1) is 1 to 50 parts by weight relative to 100 parts by weight of the polyamide resin. When the amount is less than 1 part by weight, the pattern formation ability of the polyamide resin is low. When the amount is more than 50 parts by weight, the photosensitizer per se shows high absorption, resultantly the light applied does not reach the film bottom sufficiently and a significant reduction in sensitivity results. Therefore, such amounts are not preferred.
When it is intended to allow the positive photosensitive resin composition of the present invention to have an even higher sensitivity, it is important to add, to the resin composition, a photosensitizer (B2) which is a 1,2-naphthoquinone-2-diazide-5-sulfonate or a 1,2-naphthoquinone-2-diazide-4-sulfonate, of a phenol compound having a skeletal structure represented by the following general formula (4) or (5): 
wherein R14 is hydrogen atom or an alkyl group; and R15, R16, R17, R18, R19 and R20 are each one atom or group selected from hydrogen atom, halogen atoms, hydroxyl group, alkyl groups, alkoxy groups and cycloalkyl groups, or 
wherein R21, R22, R23, R24, R25, R26, R27, R28, and R29 are each one atom or group selected from hydrogen atom, halogen atoms, hydroxyl group, alkyl groups, alkoxy groups and cycloalkyl groups.
Examples of the phenol compound constituting the skeleton of the photosensitizer (B2) used in the present invention include the followings but are not restricted thereto. 
In the photosensitizer (B2) used in the present invention, it is preferred that 80 to 100% of the hydroxyl groups of the phenol compound represented by the general formula (4) or (5) is substituted into a 1,2-naphthoquinone-2-diazide-5-sulfonate or a 1,2-naphthoquinone-2-diazide-4-sulfonate. A proportion of substitution of less than 80% is not preferred because the photosensitizer (B2) may not give any clear increase in sensitivity. Incidentally, the proportion of substitution is a proportion of substituted hydroxyl groups to the total amount of the hydroxyl groups possessed by the phenol compound represented by the general formula (4) or (5). The weight ratio of the photosensitizer (B1) and the photosensitizer (B2) both used in the present invention is preferably 0.1xe2x89xa6(B2)/(B1)xe2x89xa60.5. When the weight ratio is less than 0.1, the photosensitizer (B2) may not give any clear increase in sensitivity. When the weight ratio is more than 0.5, scum appears at the bottom of the pattern formed by development. Therefore, such weight ratios are not preferred.
To the positive photosensitive resin composition of the present invention may be added, as necessary, a dihydropyridine derivative in order to enhance the photosensitivity of the composition. As the dihydropyridine derivative, there can be mentioned, for example, 2,6-dimethyl-3,5-diacetyl-4-(2xe2x80x2-nitrophenyl)-1,4-dihydropyridine, 4-(2xe2x80x2-nitrophenyl)-2,6-dimethyl-3,5-dicarboethoxy-1,4-dihydropyridine, and 4-(2xe2x80x2,4xe2x80x2-dintrophenyl)-2,6-dimethyl-3,5-dicarbomethoxy-1,4-dihydropyridine.
In the positive photosensitive resin composition of the present invention, it is important to further use, as necessary, a phenol compound (C) represented by the following general formula (3): 
wherein R8 and R9 are each hydrogen atom or an alkyl group; and R10, R11, R12 and R13 are each one atom or group selected from hydrogen atom, halogen atoms, hydroxyl group, alkyl groups, alkoxy groups and cycloalkyl groups.
A technique of using a phenol compound in a positive resist composition is disclosed in, for example, JP-A-3-200251, JP-A-3-200252, JP-A-3-200253, JP-A-3-200254, JP-A-4-1650, JP-A-4-11260, JP-A-4-12356 and JP-A-4-12357. The phenol compounds mentioned in these literatures, however, show a small effect for sensitivity increase when used in the positive photosensitive resin composition of the present invention using a polyamide resin as the base resin. In contrast, when the phenol compound (c) represented by the general formula (3) is used in the present resin composition, the dissolution rate of the exposed portion is elevated, resulting in increased sensitivity; further, the film thickness loss of the unexposed portion which is seen when the molecular weight of the base resin is made small for sensitivity increase, is very small.
As the phenol compound (C) represented by the general formula (3), there can be mentioned the followings. However, the phenol compound is not restricted thereto. 
Among them, a compound of the following formula (9) is preferred, and compounds of the following formulas (10) and (11) are particularly preferred in view of the sensitivity and residual film ratio obtained therewith. It is preferred that the compound of the formula (10) and/or the compound of the formula (11) occupies 50% by weight or more of the total amount of the phenol compound (C). 
The amount of the phenol compound (C) used is preferably 1 to 30 parts by weight per 100 parts by weight of the polyamide resin represented by the general formula (1). When the amount is less than 1 part by weight, the sensitivity during development is low. When the amount is more than 30 parts by weight, the residual film ratio during development is extremely low; precipitation takes place during frozen storage; accordingly, such a resin composition has no practical usability. Therefore, such amounts are not preferred.
The positive photosensitive resin composition of the present invention can contain, as necessary, additives such as levelling agent, silane coupling agent and the like.
In the present invention, the above-mentioned components are dissolved in a solvent and used in a varnish state.
As the solvent, there can be mentioned, for example, N-methyl-2-pyrrolidone, xcex3-butyrolactone, N,N-dimethylacetamide, dimethyl sulfoxide, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl lactate, ethyl lactate, butyl lactate, methyl-1,3-butylene glycol acetate, 1,3-butylene glycol-3-monomethyl ether, methyl pyruvate, ethyl pyruvate and methyl 3-methoxypropionate. These solvents may be used singly or in admixture.
Description is made on the manner in which the positive photosensitive resin composition of the present invention is used. First, the composition is coated on an appropriate substrate such as silicon wafer, ceramic substrate, aluminum substrate or the like. The coating amount is such that, when used in a semiconductor device, the final film thickness after curing becomes 0.1 to 20 xcexcm. When the film thickness is less than 0.1 xcexcm, the film is unable to sufficiently exhibit its function as a protective surface film of a semiconductor component. When the film thickness is more than 20 xcexcm, it is difficult to form a fine pattern. The coating is conducted by spin coating using a spinner, spray coating using a spray coater, dipping, printing, roll coating, etc.
Then, prebaking is conducted at 60 to 130xc2x0 C. to dry the coated film, after which an actinic ray is applied thereto through a mask of given pattern. As the actinic ray, there can be used X-ray, electron beam, ultraviolet light, visible light, etc. A ray having a wavelength of 200 to 500 nm is preferred.
Then, the exposed portion is dissolved and removed with a developing solution to obtain a relief pattern. As the developing solution, there can be suitably used aqueous solutions of an alkali, or aqueous solutions obtained by adding thereto an appropriate amount of a water-soluble organic solvent (e.g. an alcohol such as methanol or ethanol) or a surfactant. The above alkali includes, for example, inorganic alkalis such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, ammonia water and the like; primary amines such as ethylamine, n-propylamine and the like; secondary amines such as diethylamine, di-n-propylamine and the like; tertiary amines such as triethylamine, methyldiethylamine and the like; alcoholamines such as dimethylethanolamine, triethanolamine and the like; and quaternary ammonium salts such as tetramethylammonium hydroxide, tetraethylammonium hydroxide and the like.
The development can be conducted by spraying, paddle, dipping, ultrasonic wave, etc.
Then, the relief pattern formed by development is rinsed. Distilled water is used as the rinsing liquid. Then, a heat treatment is conducted to form an oxazole ring to obtain a highly heat-resistant final pattern.
The positive photosensitive resin composition of the present invention is useful not only for semiconductor applications but also for interlayer insulation of multi-layer circuit or surface coating of flexible copper-clad laminate or for solder resist film, liquid crystal alignment film, etc.
The present invention is described specifically below by way of Examples.